Vacuum pump



J. B. LITTLEFIELD VACUUM PUMP Filed Feb. 1, 1939 Eff/T l.

2 Sheets-Sheet 1 541. J, B. LITTLEFIELD 2,261,263

VACUUM PUMP Filed Feb. 1, 1959 2 Sheets-Sheet 2 INVENTOR.

ATTORNEYS.

Patented Nov. 4, 1941 VACUUM PUMP John B. Littlcfieldylittsburgh Pa., assignor to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 1, 1939, Serial No. 254,020

Claims. (01. 230-24) This invention relates to vacuum pumps, and moreparticularly to pumps capable of variable speed operation.

For some purposes it is desirabl tomaintain a uniform, or substantially uniform, degree of vacuum but this is difiicultto do with pumps which are operated in any way, for example manually, in which the rate of operation varies, because the suction created varies as the pump is operated faster or more slowly. The maintenance of a uniform reduced pressure, or vacuum, is important, for example, in the sampling of atmospheres by the impinger method to determine the number of dust particles in a givenatmosphere. In that method dust-laden air is drawn through a dustcollecting device, called an impinger, by asuction-creating device or vacuum pump. The impinger comprises a receptacle containing a predetermined volume of a liquid through which the air is drawn and in which dust is deposited so that the particles can be 'countedlater. To practice the impinger method successfully and to provide comparable results, a certain volume of air must be drawn through the impinger per unit of time, and this requires a uniform suction throughout; the sample-taking period, usually five minutes. 7 There is no particular problem in maintaining uniform suction when using pumps driven electrically or by compressed air, but because of the bulk, weight, and power requiremerits of such pumps they are unsuited for use in small, portable, hand-operated midget impinger apparatus such as is needed for plant and field Work. I-Ieretofore it has been diflicult to maintain uniform suction with the manuallly operated apparatus because of the difficulty. in;operating the pump at a uniform rate of speed.

It is among the objects of this invention to provide a vacuum pump which automatically maintains substantially uniform suction regardless of normal variations in the speed at which itis operated, which is adjustable for producing different degrees of suction, and which is simple and inexpensive in construction. Another objectis to provide such a pump that is especialy suitable for use with midget impingers.

In accordance with this invention a vacuum pump housing is provided with a chamber with which suitable variable speed means, such as manually actuated pistons, are connected in such a way that their movements reduce the air pressure in the chamber. The side wall of the chamber is provided with an inlet orifice adapted to be connected with any device, such as an impinger,

through or from which it is desired todraw air.

Means responsive to variations in the reduced air pressure in the housing chamber, or to pressure variations caused by the externalmeans to which the pump is connected, varies the effective size of the orifice in accordance with those pressure var-' iations. For example, if the pump is operated rapidly so that air pressure in the housing chamber is reduced a relatively great amount, the effective size of the orifice is automatically reduced to such an extent that the suction at its outer end remains substantially the same as it is when the pump is operated at a slower rate and the effective size of the orifice is greater. The orificecontrolling means is adjustable so that any desired suction can be maintained at the outer end of the orifice.

The preferred embodiment of the invention is illustrated in the accompanying drawings which Fig. l is a plan view of a case containing impinger apparatus including my improved vacuum pump; Fig. 2 isa side view of the apparatus when thecase is open and with the vacuum pump partly in section; and Fig. 3 is an enlarged vertical section of the pump on the line III-III of Fig. 2. r

Although myinventon is shown in connection with impinger apparatus, this is done .solely for the purpose of illustration. It will therefore be understood that the invention isapplicable wherever it is desirable to maintain a uniform suction by a vacuum pump which is likely to be operated at varying rates of speed.

Referring to Figs. 1 and'2 of the drawings, a carrying case I is provided with a hinged cover 2 and with metal loops 3 for .a carrying strap. Mounted in one end of the case is a vacuum pump, and in the other end is a group'of impingers. Each impinger consists of a cylindrical glass sampling tube l having a 'closed'fiat bottom and an upwardlyv extending side arm 6 near its top. The upper end of the sampling tube is closed by a stopper 1 provided with an axial opening inlwhicha glass tube 8 is disposed. When not in use, the upper end of tube 8 is closed by a rubber cap 9, and the upper end of arm 6 by a rubber cap 12. The sides of the bottle are graduated, and the lower end of tube 8, which is provided with an opening 1 mm. infdiameter, is spaced about 5mm. from the bottom of the sampling tube. The sampling tube is filled to the, 10 ml. markwith a suitable liquid, preferably ethyl or normal propyl alcohol. As shown in Fig. 2, the impingers are held in upright position in recesses I4'.;of a'woodenblock l3. Block [3 is held against the bottom of the caseby a pair of bracloets, one of which, I6, is attached to the end wall of the case and overlies the block, while the other, H, is secured to the bottom of the case and projects into a slot l8 in the side of the block. The block can therefore be slid in and out of the case when the cover is open.

The vacuum pump, fastened to the back of the case, comprises a metal housing including a central hub portion 2| which is hollow to provide a central cylindrical surge chamber 22, and four radial cylinders 23 which are 90 apart. The outer end of each cylinder is closed by a head 24 threaded thereon. Slidably mounted in each cylinder is a piston 26 provided with a transverse slot 21 in which one end of a connecting rod is pivoted. The inner ends of three connecting rods 28 are connected by pivot pins 29 to a cylindrical mother bearing 3| in chamber 22, the fourth connecting rod 32 being rigidly connected to the bearing by two pins 33 so that the bearing can not rotate about a single throw crank 36 to which the bearing is connected by a pin 34. Crank 36 is keyed to a shaft 31, Fig. 3, which extends through the rear wall of the pump housing and projects from the back of the case where it receives a crank handle 38 that i pivotally mounted thereon so that its handle can be swung upwardly over the top of the case when the apparatus is not in use (Figs. 1 and 2). Turning of crank handle 38 causes shaft 31 and crank 36 to move bearing 3| in a circular path between the guiding inner faces of the crank and a boss 39 in the center of the opposite wall of the surge chamber, whereby the pistons are reciprocated successively in the four cylinders.

Each piston is provided with a plurality of passages 4| the outer ends of which are normally closed by a flexible diaphragm 42 secured at its center to the piston, and cylinder heads 24 are likewise provided with a plurality of passages 43 which are normally closed in the same manner by flexible diaphragms 44. Consequently, as a piston moves down in the cylinder air is forced outwardly through passages 4| into the space between the piston and the cylinder head. When the piston moves upwardly this air is forced out through passages 43. By this action the pressure in the surge chamber is reduced so that the pump acts to create vacuum.

Boss 39 is formed integrally with a cover member 46 for the front of surge chamber22, as shown in Fig. 3. The side wall of the cover member is provided with a nipple 41 which may be connected by a flexible hose 48 to side arm 6 'of an impinger or other device to which vacuum is to be applied. Air or other fluid being pumped passes through nipple 41' into a chamber 22a formed in part by cover member 46, and thence into surge chamber 22 through air inlet orifice 49 formed in a nut member mounted centrally of boss 39.. v

' It is a major feature of this invention that the effective sizeor orifice 49 is varied in accordance with variations in the reduction of air pressure in the surge chamber, or with brief pressure variations in, chamber 22a caused by'diiferences in impingers or the like, so that the suction produced in chamber 22a will remain substantially constant regardless of the degree of pressure reduction in the chamber. This is accomplished by tapering orifice 49 to provide a seat for a tapered needle which is resiliently mounted so as to' respond to variations of pressure within chamber 2212. In the embodiment shown a tapered needle valve .member 5| is mounted in a flexible diaphragm member 52, suitably of rubber, that is clamped peripherally between the faces of cover member 46 and a cover plate 53, as seen in Fig. 3, so that the diaphragm is free to flex under pressure variations. Diaphragm 52 cooperates with member 46 to complete chamber 22a. Screws 54 hold the cover plate 53 and cover member 46 to housing.2l. Cover plate 53 is provided with an opening 55 so that the outer face of the diaphragm is exposed to atmospheric pressure. Orilice 49 is, of course, tapered complementarily to needle 5|.

Upon the occurrence of pressure changes within chamber 22a, the pressure differential on the opposite sides of the diaphragm 52 will cause the diaphragm to flex inwardly or outwardly, as the case may be, thus decreasing or increasing the elTective size of orifice 49 and thereby maintaining substantially uniform suction at nipple 4'1.

To permit any desired degree of suction to be maintained, means are provided for increasing the resistance of the diaphragm to flexure. For this purpose the outer end of needle 5| is provided with a threaded stem 55 which projects outwardly from the diaphragm through a larger central opening in cover plate 53. Mounted on this stem is a coil spring 51 which is compressed between the cover plate and a nut 58 threaded on the stem. By adjusting the nut upon the stem, the' pressure exerted by the coil on the diaphragm can be varied, thus varying the prwsure (or vacuum) at which the needle will respond.

To provide for ready and simple storage of flexible hose 48, and also to guard adjusting nut 58 against being moved accidentally, a spool 59, Fig. 3, is connected to cover plate'53. The hose can be wound on or off this spool readily when case cover 2 is opened, and after being unwound it is inserted in a slot 60 in the case, permitting cover 2 to be closed while'the apparatus is inuse. Fig. 1 indicates the hose wound on the spool.

In the embodiment shown a vacuum gauge 6| mounted in the top of the case is connected by 5 a flexible hose 62 to a second nipple 63, Fig. 2,

mounted also in the side wall of cover member 46. This permits the operator to know that the pump" is operating at the desired vacuum. Also, the gauge is used when it is desired to change the operatin pressure by adjustment of nut 58.

The above-described dust-sampling apparatus is calibrated to give a sampling rate of 0.1 cubic foot of air per minute at a gauge reading of 12 inches of water vacuum through an impinger having ajl mm. orifice. This rate of suction is maintained aslong ts the crank speed "is high enough (about 50 revolutions per minute) to keep the gauge pointer stationary. If the crank is turned faster the sampling rate is not increased because the diaphragm 52 moves inwardly thus moving needle 5| into orifice 48 and effectively reducing its area. Thereverse result follows when the crank is operated more slowly. In case the demandf upon regulating chamber 22a Varies, as where th pump is quickly changed from an impinger having an opening of one size to one having a difierent sized opening, the tendency of the vacuum in the regulating chamber to chang will be quickly arrested by flexure of the diaphragm either toward or away from orifice 49.

The entire apparatus weighs only a few pounds, whereby it is readily portable. It does not de- The acemes sim'p licity and relative inexpensiveness of the ap- "operation of my invention, and have illustrated and described what'I now consider to" represent its bestembodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than asspecifically illustrated and described; I"1

1. Avacuum pump comprising a'housing provided with a chamber having an inlet orifice in itsside wall,'*means"'for reducing air pressure in said chamber, and means actuated byvariations in said reduced pressure for varying-the effective 'size of said orifice to' thereby maintain a-subst'antia-lly constant suction at its outer end regardless of the exterit to which the air pressure in said. chamber is reduced a 1 I 2. A vacuum pump comprising a housing'provided with achamber having-a side wall provided with aninlet orifice, means for reducing air'pressure in said chamber, a diaphragm adapted to be flexed by pressure variations in said chamber, and means carried by the diaphragm for varying th effective size of said orifice to thereby maintain a substantially constant suction at its outer end regardless of the extent to which the air pressure in said chamber is reduced.

3. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, means actuated by variations in said reduced pressure for varying th effective size of said orifice to thereby maintain a substantially constant suction at its outer end regardless of the extent to which the air pressure in said chamber is reduced, and means for adjusting the resistance of said orifice-varying means to actuation by said reduced air pressure.

4. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, a diaphragm adapted to be flexed by variations in said reduced pressure, means rigidly carried by the diaphragm for varying the effective size of said orifice to thereby maintain a substantially constant suction at its outer end regardless of the extent to which the air pressure in said chamber is reduced, and adjustable means for increasing the resistance of said diaphragm to being flexed.

5. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, means actuated by variations in said reduced pressure for varying the efiective size of said orific to thereby maintain a substantially constant suction at its outer end regardless of the extent to which the air pressure in said chamber is reduced, resilient means for biasing said orifice-Varying means away from th orifice, and means for adjusting the pressure exerted by said resilient means.

6. A vacuum pump comprising a housing provided with a chamber having an inlet orifice in its side wall, means for reducing air pressure in said chamber, a diaphragm adapted to be flexed by variations in air pressure, means carried by the diaphragm for varying the efiective size of said orifice when the diaphragm is flexed, a stem rigidly connected to the opposite side of the diaphragmaa:coilsprmg encircling the stem, fixed means engaging one e'nd'l'of the spring,- and adjustable means engaging the opposite end of the spring,"one ofsaid spring-engaging means being "mounted-on saidstem and the other being slidable relative thereto.

A 'vacu'urn pump 'comprisingfa housing provided with a chamber having a side wall provided with an inwardly tapered inlet orifice,

means'f or reducing air pressure in said chamber, a diaphragm adapted to be flexed by pressure variations-in said chamber', and a tapered neevided with a chamber having an inlet orifice in its side wall, means'for reducing air pressure in said chamber, a hollow casing surrounding the outer end of said orifice and provided with an inlet opening, and means mounted'in said casing and adapted to be actuated by the tendency of -the pressure in said casing to vary for varying the efiective size of said orifice to thereby maintain a substantially constant degree of low pressure in said casing.

9. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, a hollow casing surrounding the outer end of said orifice and provided with an inlet opening, a diaphragm mounted in said casing and adapted to be flexed by the tendency of the pressure in said casing to vary, and means carried by the diaphragm for varying the effective size of said orifice to thereby maintain a substantially constant suction in said casing.

10. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, a hollow casing surrounding the outer end of said orifice and provided with an inlet opening, a diaphragm mounted in said casing. and adapted to be flexed by the tendency of the pressure in said casing to vary,a threaded stem connected to the diaphragm and projecting loosely through an opening in said casing, a coil spring encircling the portion of the stem projecting from the casing, a nut threaded on the stem and bearing against the outer end of the spring, and means carried by the diaphragm for varying the effective size of said orifice to thereby maintain a substantially constant suction at its outer end.

11. An automatic suction, regulator for vacuum pump having an inlet orifice, comprising a valve projecting into said orifice, and a flexible diaphragm carrying said valve and responsive to variations in pressure in said pump for maintaining a substantially constant suction at the outer end of said orifice.

12. An automatic suction regulator for a vacuum pump having an inlet orifice, comprising a valve projecting into said orifice, a flexible diaphragm carrying said valve and responsive to variations in pressure in said pump for maintaining a substantially constant suction at the outer end of said orifice, and adjustable recomprising a housing provided with a central surge chamber and a plurality of cylinders radiating therefrom, a piston in each cylinder, the pistons and the cylinder heads being provided with check valves, manually operable means for reciprocating said pistons to reduce air pressure in the surge chamber, the wall of said chamber being provided with an inlet orifice, a fiexible diaphragm mounted adjacent the outer end of said orifice and responsive to pressure variations at that end of the orifice, and means carried by the diaphragm for varying the effective size of said orifice in accordance with the flexing of the diaphragm.

14. A vacuum pump for use with an impinger comprising a housing provided with a central surge chamber and a plurality of cylinders radiating therefrom, a piston in each cylinder, the pistons and the cylinder heads being provided with check valves, manually operable means for reciprocating said pistons to reduce air pressure in the surge chamber, the wall of said chamber being provided with an inlet orifice, a flexible diaphragm mounted adjacent the outer end of said orifice and responsive to pressure variations at that end of the orifice, means carried by the diaphragm for varying the effective size of said orifice in accordance with the flexing of the diaphragm, and a vacuum gauge operatively connected to said chamber.

15. A vacuum pump comprising a housing provided with a chamber having a side wall provided with an inlet orifice, means for reducing air pressure in said chamber, a hollow casing surrounding the outer end of said orifice and provided with an inlet opening, a diaphragm mounted in said casing and adapted to be flexed by the tendency of the pressure in said casing to vary, a threaded stem connected to the diaphragm and projecting loosely through an opening in said casing, a coil spring encircling the portion of the stem projecting from the casing, a nut threaded on the stem and bearing against the outer end of the spring, means carried by the diaphragm for varying the efiective size of said orifice to thereby maintain a substantially constant suction in said casing, a flexible tube connected to said inlet opening, and a spool surrounding said projecting portion of said stem and adapted to receive coils of said tube.

JOHN B. LITTLEFIELD. 

